Molecular Genetics of Prokaryotes

1. Which of the following is not part of the lac operon of E. coli?

A. genes for inducible enzymes of lactose metabolism
B. genes for the repressor, a regulatory protein
C. gene for RNA polymerase
D. a promoter, the RNA polymerase binding site
E. the operator, the repressor binding site

2. (The role of the inducer of the lac operon). The inducer:

A. combines with a repressor and prevents it from binding to the promoter
B. combines with a repressor and prevents it from binding to the operator
C. binds to the promoter and prevents the repressor from binding to the operator
D. binds to the operator and prevents the repressor from binding at this site
E. binds to the termination codons and allows protein synthesis to continue

3. An E. coli strain is lac Z-. The structural gene for à?-galactosidase is encoded at the lac Z locus. How would you describe the regulation of lactose metabolism in these cells?

A. normal regulation of lactose metabolism
B. constitutive expression of lac Z+
C. inability to synthesize the lac Z+ gene product, à?-galactosidase
D. lac Z+ gene is inducible, but unable to be repressed by high glucose
E. no synthesis of the lac I gene product, the lac repressor

4. Cells of an E. coli strain that are trp- lac Z-met+bio+were mixed with cells of an E. coli strain that are trp+lac Z+ met- bio-and cultured for several hours. Then cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these few cells become trp+ lac Z+ met+bio+?

5. An E. coli strain is F- lac Z- met+ bio+. Cells from this strain are mixed with an E. coli strain that is lac Z+ met- bio-and carrying an F' episome with the Plac O+ lac Z+ DNA sequence on the episome, and cultured for several hours. Then cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these few cells become lac Z+ met+ bio+?

6. How many lac Z genes were present in the cells described in problem 5 that were able to grow on minimal media?

A. Only 1, the lac Z- allele on the bacterial chromosome.
B. Only 1, the lac Z+ allele on the bacterial chromosome.
C. Two, the lac Z- allele on the bacterial chromosome and the lac Z+ allele on the bacterial chromosome. Two, the lac Z- allele on the bacterial chromosome and the lac Z+ allele on the bacterial chromosome.
D. Two, the lac Z- allele on the bacterial chromosome and the lac Z+ allele on the F' episome
E. Only 1, the lac Z+ allele on the F' episome

7. How would you describe the regulation of lactose metabolism in the cells described in problem 5 that were able to grow on minimal media with lactose as a nutrient?

A. normal regulation of lactose metabolism
B. constitutive expression of lac Z+
C. inability to synthesize the lac Z+ gene product, b-galactosidase
D. lac Z+ gene is inducible, but unable to be repressed by high glucose
E. no synthesis of the lac I gene product, the lac repressor

8. An E. coli strain that is lac Z- is conjugated with E. coli cells carrying an F' plasmid with the Plac Oc- lac Z+ DNA sequence on the episome. The Oc is a mutation of the lactose operator that is no longer able to bind the lac I gene product which codes for the lac repressor. How would the expression of the lac Z+ be regulated in the resulting cells that are diploid for the lactose regulatory region and the lac Z gene?

A. normal regulation of lactose metabolism
B. constitutive expression of lac Z+
C. inability to synthesize the lac Z+ gene product, à?-galactosidase
D. lac Z+ gene is inducible, but unable to be repressed by high glucose
E. no synthesis of the lac I gene product, the lac repressor

9. An E. coli strain is lac I- The lac I+ DNA sequence encodes the lactose repressor. How would you describe the regulation of lactose metabolism in these cells?

10. An E. coli strain that is lac I- is conjugated with E. coli cells carrying an F' plasmid with the PI -lac I+DNA sequence on the episome. How would the expression of the lac Z+be regulated in the resulting cells that are diploid and heterozygous for the lac I gene (lac I+ on episome and lac I-on the bacterial chromosome)?

A. normal regulation of lactose metabolism
B. constitutive expression of lac Z+
C. inability to synthesize the lac Z+ gene product, à?-galactosidase
D. lac Z+ gene is inducible, but unable to be repressed by high glucose
E. no synthesis of the lac I gene product, the lac repressor

11. Bacteria utilize glucose first, even if other sugars are present, through a mechanism called:

12. An E. coli cell is grown in the presence of high amounts of glucose. Which of the following is true?

A. The cell will utilize lactose as a carbon source exclusively
B. The level of cyclic-AMP in the cell will be low
C. The level of cyclic-AMP in the cell will be high
D. Transcription of mRNA from the lac operon will be high
E. The cell will be forced to carry out fermentation

13. Which of the following growth media would you expect to result in synthesis of high levels of mRNA for the enzymes of the E. coli lac operon?

A. high glucose, high lactose
B. no glucose, no lactose
C. high glucose, low lactose
D. no glucose, high lactose
E. none of these

14. An E. coli cell is grown in the absence of glucose. Which of the following will be true?

A. The level of cyclic-AMP will be low
B. The CRP protein cannot bind to the DNA
C. If lactose is present, lac mRNA synthesis will occur at a high level
D. The cell will manufacture glucose by fixing carbon dioxide
E. The cell will be forced to carry out fermentation

Thank you!

Solution Preview

1. Which of the following is not part of the lac operon of E. coli?

A. genes for inducible enzymes of lactose metabolism
B. genes for the repressor, a regulatory protein
C. gene for RNA polymerase
D. a promoter, the RNA polymerase binding site
E. the operator, the repressor binding site

2. (The role of the inducer of the lac operon). The inducer:

A. combines with a repressor and prevents it from binding to the promoter
B. combines with a repressor and prevents it from binding to the operator
C. binds to the promoter and prevents the repressor from binding to the operator
D. binds to the operator and prevents the repressor from binding at this site
E. binds to the termination codons and allows protein synthesis to continue

3. An E. coli strain is lac Z-. The structural gene for à?-galactosidase is encoded at the lac Z locus. How would you describe the regulation of lactose metabolism in these cells?

A. normal regulation of lactose metabolism
B. constitutive expression of lac Z+
C. inability to synthesize the lac Z+ gene product, à?-galactosidase
D. lac Z+ gene is inducible, but unable to be repressed by high glucose
E. no synthesis of the lac I gene product, the lac repressor

4. Cells of an E. coli strain that are trp- lac Z-met+bio+were mixed with cells of an E. coli strain that are trp+lac Z+ met- bio-and cultured for several hours. Then cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these few cells become trp+ lac Z+ met+bio+?

A. transformation
B. ...

Solution Summary

This solution provides the correct answers for the multiple choice quiz on Molecular Genetics of Prokaryotes. An explanation for each correct answer is also provided.